Endocrine Lecture 24

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Posterior Pituitary Gland

Neurohypophysis

Posterior Pituitary Gland

-Does not synthesize hormones
-Consists of axon terminals from two groups of hypothalamic neurons
-These neurons release two peptide hormones that enter capillaries: ADH or vasopressin, Oxytocin (OT)

Hypothalamus

Antidiuretic hormone (ADH) and oxytocin made in the --- are transported into the neurosecretory vessicles where they are stored until a signal comes to stimulate release

Antidiuretic Hormone

--- produced by cells in supraoptic nucleus in the hypothalamus in response to signals from osmoreceptors

Antidiuretic Hormone

-Prevents diuresis--decreases urine production by stimulating the kidneys to return more water back into the blood
-Prevents water loss in sweat glands
-Causes constriction of arterioles (Vasopressin)

Antidiuretic Hormone

Regulation of ---
Dehydration or high osmolarity of blood - ADH released from posterior pituitary
Overhydration or low osmolarity of blood - ADH release inhibited
ADH release inhibited by alcohol
A lack of ADH results in diabetes insipidus - inability of the kidneys to conserve H2O, excessive urination

Oxytocin

Produced by cells in the paraventricular nucleus of the hypothalamus
Target tissues: uterus: during labor
Mammary glands: after delivery

Oxytocin

Regulation during Labor
-Stimulation of uterus by baby's head causing stretch of cervix
-Oxytocin release from posterior pituitary
-Uterine smooth muscle contracts
-As the baby's head is pushed into the cervix, oxytocin release increases
-Muscle contraction, which pushes the baby further and elicits even more oxytocin release
- When baby is born, the positive feedback loop ceases

Oxytocin

Regulation after delivery
-Mammary glands
-Suckling & hearing baby's cry stimulates oxytocin release
-Oxytocin causes muscle contraction & milk ejection
Lactation is the process of milk production and ejection
-milk production is stimulated by prolactin
-Polactin and Oxytocin work together in lactation

Follicular cells

Produce Thyroid Hormones
T3 - Triiodothyronine
T4 - Thyroxine or tetraiodothyronine

Thyroid Hormones

Formation of ---:
-Iodide trapping by follicular cells
-Synthesis of TGB into colloid
-Iodination of tyrosine in colloid
-Formation of T3 & T4 by combining T1 and T2 together
-Uptake & digestion of TGB by follicle cells
-Secretion of T3 and T4 into blood; binds to thyroid binding globulin (TBG)

Thyroid Hormones

Actions of ---:
-Increase Basal Metabolic Rate by stimulating the cellular use of O2 to produce ATP -> increased cellular catabolism of glucose (glycolysis), fatty acids (beta oxidation) and triglycerides (lipolysis)
-Increase synthesis of Na/K ATPase -> more ATP is used to pump ions -> ATP use produces heat, which raises body temperature -> called the calorigenic effect

Thyroid Hormones

Actions of ---:
-Enhance some actions of sympathetic nervous system by up-regulating beta-receptors -> increased heart rate, contractility and blood pressure
-Stimulate growth (in conjunction with hGH and insulin) particularly during development

Hyposecretion

Thyroid Gland Disorders ---:
-During development, infancy and/or early childhood results in dwarfism and severe mental retardation (congenital hypothyroidism or cretinism)
-In the adult results in edema, low heart rate, muscle weakness, sensitivity to cold, low body temperature, weight gain and mental dullness (myxedema)

Hypersecretion

Thyroid Gland Disorders ---:
-Hyperthyroidism (Graves' disease): weight loss, nervousness, tremor, increased heart rate and blood pressure, exophthalamos (edema behind eyes), high body temp, sweating

Goiter

Thyroid Gland Disorders ---:
-Enlarged thyroid (lack of iodine)
-occurs because TSH levels are high -> stimulates growth of thyroid gland
-can be associated with hyperthyroidism, hypothyroidism or eithyroidism
-dietary lack of iodine leads to low thyroid hormone (T3/T4) production -> stimulates TSH by negative feedback -> stimulates thyroid gland growth

Calcitonin

Secreted by parafollicular cells of the thyroid gland. Lowers blood Ca2+ levels by inhibiting osteoclasts

Parathyroid Hormone

secreted by chief cells of parathyroid gland. Raises blood Ca2+ levels by stimulating osteoclasts

Parathyroid Hormone

-Raises blood calcium levels
-Increases activity of osteoclasts
-Increases reabsorption of Ca2+ by kidney
-Inhibits rabsorption of phosphate (HPO4)-2
-Promotes formation of calcitriol (active vitamin D3) by kidney which increases absorption of Ca2+ and Mg2+ by intestinal tract

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